1. Field of the Invention
The present invention relates to a display device having a light emitting element, and a driving method of the same.
2. Description of the Related Art
In recent years, research and development have been advanced on a display device having a light emitting element (self-luminous element). Such a display device is widely used as a display of a portable phone and a monitor of a personal computer by taking advantages of high image quality, thinness, and lightweight. In particular, such a display device has features such as high response, low voltage, and low power consumption that are suitable for displaying a moving image. Therefore, it is expected to be applied to a wide range of devices including a new generation of portable phone and a portable information terminal (PDA).
Luminance of the light emitting element degrades gradually over time. For example, a predetermined luminance which is obtained with a certain voltage Vo and a certain current Io cannot be obtained with the same voltage Vo any more because only the current Io′ is supplied to the light emitting element due to the degradation over time. Further, the same luminance cannot be always obtained with a certain current due to the degradation over time of the light emitting element.
This is because the light emitting element generates heat by receiving voltage or current, which changes the qualities of surface of the film over the light emitting element and surface of the electrode. Further, as the light emitting elements variously changes the conditions in each pixel, an image persistence may appear.
In order to enhance the reliability by suppressing the degradation of the light emitting element, which is one of the changed conditions, it is suggested that a reverse voltage which is in the opposite direction to the voltage applied to the light emitting element when it emits light is applied to the light emitting element (refer to Patent Document 1).
[Patent Document 1]
Japanese Patent Application Laid-Open No. 2001-117534